Thermal analyzers are utilized to test and measure characteristics of materials at various temperatures. Materials undergo significant changes at various temperatures over a wide temperatures range. For example, characteristics such as size, color, weight, electrical and magnetic properties and the like may change significantly at one or more temperatures to which a sample is heated or cooled. It is important to know the precise temperatures at which these characteristics undergo change.
The sample materials to be tested are disposed in a furnace or oven and heated or cooled over a temperature range during analysis. However, due to such effects as poor thermal coupling, thermal gradients, oven geometry and the like, the temperature of the test sample and the oven can be different. This temperature difference is normally minimized by manually calibrating at two points within the measurement temperature range. Thus, at two points actual sample temperature is made equal to the required sample temperature by raising or lowering the oven temperature. This is a tedious and time consuming method since calibration at one point disturbs calibration at the other point and much trial and error manipulation is required before adequate calibration is achieved manually. After calibration, it is known at what temperature the oven must be maintained at the calibration points to keep the sample at the selected temperature at those points. When the selected sample temperature is not at one of the calibration points, the offsets at both calibration points are used to progressively affect the oven temperature to maintain the sample at the approximate required temperature.
The present invention contemplates a thermal analyzer system having means for automatically calibrating the system wherein the sample and programmed temperature are made equal at three points and which approximates a correction for the rest of the temperature scale.